The invention is directed to a circular knitting machine having a frame in which a first carrier for knitting tools, a first cam assigned to the latter, a second carrier for knitting tools arranged above the first carrier, and a second cam assigned to the latter are mounted in such a way that changes in temperature result in an unwanted change in a comb distance measured in the direction of the machine axis and defined by the two carriers and one of the two carriers and the associated cam are supported so as to be displaceable in the direction of the machine axis.
In circular knitting machines of this type (e.g. DE-OS 17 60 124 and DE-OS 22 12 749) which have two needle carriers or beds and can be constructed as right/right circular knitting machines or interlock machines as well as double-cylinder machines, the reed or comb distance between the needle cylinder and the dial or rib disk, sometimes also called verge distance, and the strength or length of the stitches determined by it, vary depending on whether the machine is cold or warm, particularly in machines which generate high heat. Thus, knitted fabrics having varying stitch lengths are produced. This is generally the case in circular knitting machines which have a large number of knitting systems, are operated at high speed, have high gauges (number of knitting tools per inch) and/or develop a comparatively high friction between the knitting tools (needles, jacks, sinkers, etc.) and the respective cam parts.
The difference in comb distance results from the fact that the needle cylinder, which is generally supported in a frame by its lower end, increasingly expands axially upward when the machine is running warm or during other changes in temperature, whereas the dial or rib disk which is generally suspended at an upper frame part expands downward simultaneously. Because of this, or even as a result of only one of these two effects, the comb distance is increasingly reduced during warming and is smaller in warm running machines than in cold machines. Although these unwanted changes are comparatively small, e.g. in the order of magnitude of only several hundredths of a millimeter, they nevertheless have a significant influence on the operation of the circular knitting machine and on the quality of the knitted fabrics produced with it.
A result of this phenomenon is e.g. that a circular knitting machine whose comb distance has been adjusted in the warm state causes problems when started cold because the knitting tools consume more thread, the thread tension is correspondingly greater and the threads can even break. The machine must then be switched off, manually readjusted by an axial relative displacement of the dial and/or needle cylinder or by increasing the thread feed and then restarted. However, both of these adjustments are inadequate because they change the size of the stitch and the fabric quality and because the same adjustments would therefore have to be made in reverse after the machine has warmed up to maintain the stitch length and fabric quality actually desired in both a warm and a cold machine. It would therefore be ideal if the comb distance could be maintained constant independently of the respective machine temperature.
Similar problems result in circular knitting machines in which a sinker ring is securely connected with the upper end of the needle cylinder. In this case, however, the stitch size increases when the machine is running warm because the distance between the sinkers and the cylinder cam changes when the needle cylinder expands. Therefore, the known devices for preventing this problem (DE-OS 26 40 112, DE-OS 32 32 643 and DE-OS 33 16 382) can not easily be used to maintain a constant comb distance.